Inclusion body myositis and Welander distal myopathy: a clinical, neurophysiological and morphological comparison.

Five patients with inclusion body myositis (IBM), an acquired inflammatory myopathy, and five patients with Welander hereditary distal myopathy (WDM) were compared clinically and with neurophysiological and morphological techniques. Both diseases have a late insidious onset, but the course of IBM is more severe. IBM mainly affects proximal muscles in the lower extremities, while distal muscle groups are involved in both upper and lower extremities. In WDM there is always a strict distal muscle involvement. The neurophysiological characteristics of the two conditions include both myopathic and neurogenic components. In both diseases there were rimmed vacuoles in muscle fibres and at the ultrastructural level cytoplasmic 15-18 nm filamentous inclusions. Although the histopathology of muscle in IBM and WDM has some common features, inflammatory infiltrates were never found in WDM. Such infiltrates seem to be an important clue to the correct diagnosis of IBM.